London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

As scores of newspaper photographers were staging a protest outside New Scotland Yard on Monday, a former British spy chief was giving them her tacit support. Dame Stella Rimington, the one-time head of MI5, gave a candid interview to a Spanish paper in which she bemoaned the increasing restrictions of civil liberty in Britain.

The Government was threatening human rights, she said, by exploiting fear of terrorism to introduce laws interfering with people's privacy. She referred explicitly to a belief that Britain is becoming "a police state".

Plenty of journalists have said much the same - notably Henry Porter in The Observer, who has done his best in recent years to highlight the many threats to our freedom. Taking Liberties, a DVD made by Chris Atkins, is also a full-frontal assault on this Government's authoritarian lawmaking.

For press photographers who meet police officers on a daily basis, curtailments of freedom have become increasingly obvious since 9/11 - especially since the July 2005 bombings in London.

There have been many more clashes between the people in waxed jackets and those in the blue uniforms. But the traditional pettifogging differences of opinion between press and police at news events have sometimes escalated into confrontations leading to photographers being arrested. A video produced last September by the National Union of Journalists, Collateral Damage, showed several instances of photographers being prevented from doing their work by police.

Now this week's introduction of Section 76 of the Counter-Terrorism Act gives police new powers of constraint. It makes it an offence to "elicit, publish or communicate information" relating to members of the armed forces, intelligence services and police which is "likely to be useful to a person committing or preparing an act of terrorism".

It has the potential to turn newspaper photographers and TV camera operators into lawbreakers, by making it illegal to take pictures or shoot film that feature police, even if in plain clothes. As one photographer remarked: "How are we supposed to know who they are?"

No wonder the Metropolitan Police Federation (MPF), which represents 26,000 officers, has offered its support to photographers. It believes, as newspaper bodies argued during the Act's passage through Parliament, that it is so poorly drafted as to be, at best, unworkable and, at worst, likely to inhibit press freedom.

Nigel Howard, one of four Evening Standard photographers who joined the Monday protest, said: "This is a threat to bona fide newsgatherers and even innocent tourists. If I picture Gordon Brown and happen to include members of the Special Escort Group who accompany him, I am now liable to arrest."

Guardian photographer Martin Argles, who also attended the demonstration, believes the law is bound to lead to misunderstandings between photographers and police who try to implement the letter of the law. He said: "There could be unfair arrests. We might be ordered to delete images."

The very idea of photographers being told what they can and cannot picture, or of having their pictures deleted, smacks of totalitarianism, reminding us of certain high-handed acts of official censorship in China during the build-up to the Olympics.

Yet the Government had fair warning. Newspaper editors and TV executives warned ministers of the likely consequences of enacting Section 76.

Some lawyers feel journalists engaged in normal newsgathering ought not to fall foul of the new law because they will have a defence of "reasonable excuse". But photographers I have spoken to point out that officers already interpret laws very differently on the ground. Some are helpful to photographers while others intimidate them.

Howard said: "There is no clear policy. A change of shifts at the scene of a crime, for instance, can lead to a change in the way we are dealt with." This goes beyond the good cop/bad cop scenario, however. By the nature of their work, if photographers are prevented from taking pictures at a news event, they cannot go back after winning their cases in court. The moment has passed.

Photographers have also faced requests from uniformed police not to take their pictures because, they say, they also do undercover work. The logic of this argument is that no police officer could be pictured at any time.

What this law does is turn what have been informal requests into potentially much more formalised demands. Inevitably, there is going to be some kind of test case in which the Director of Public Prosecutions will have to decide whether to make a case against a photographer. This seems very unlikely indeed, making a nonsense of the law.

There is another odd aspect to all this. When the Tube and buses were bombed on 7/7, the police asked members of the public if they could provide images from their cameras and mobile phones that might help solve the crime. Yet the police are now expected to prevent people from taking pictures that might conceivably prove of value to them.

One sensible solution - apart from the unlikely rescinding of the legislation - was touted last year by Austin Mitchell MP. He called for the introduction of a photography code to enable everyone, photographers and police officers, to do their jobs without unnecessary conflicts.

In spite of Section 76, that might still prove a useful tool. It will become essential once we arrive at the 2012 Olympics in London, an event that will be subject to an intense security operation.

How can press photographers, and tourists, avoid taking pictures of police, possibly including Special Branch operatives, in such circumstances? The law that seeks to prevent them doing so is an ass.